JP2002311136A - Method and sonar for detection of buried object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that two kinds of low-frequency and high-frequency sonars must be operated simultaneously when an object on the face of the seabed and an object under the face of the seabed are detected simultaneously so as to judge whether a target to be detected exists on the seabed or under the seabed and that an apparatus becomes large-sized and complicated. SOLUTION: An echo sounder transducer array is divided into two parts in the vertical direction, a cross-correlation processing operation between obtained received signals is performed, and the lag time which can obtain its peak is recorded in a time-series manner. At the same time, regarding an echo from the face of the seabed, the theoretical lag time which is derived from the altitude of the seabed, a range, the angle of inclination of the echo sounder transducer or the like is calculated and recorded. A point in which the echo level of a received signal exceeds a threshold value is judged to be the target. The difference between both lag times in the point of the target is detected. When its absolute value becomes the threshold value or more, the target is judged to be a target which is buried in the seabed. When the absolute value is within the threshold value, the target is judged to be a target exposed on the face of the seabed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for searching for and detecting an object buried on the sea floor or the like, and more particularly to a method for detecting a buried object and a sonar for detecting a buried object capable of distinguishing an exposed object from a buried object based on azimuth detection.

[0002]

2. Description of the Related Art In a current seabed survey, a side scan sonar and a sub-bottom profiler are widely used. Side Scan Sonar (SS
S: Side-Scan Sonar) is characterized by using a high-frequency narrow beam to visualize an acoustic shadow corresponding to the unevenness of the sea floor. In order to search for an exposed object (hereinafter, also referred to as an exposure target) on the sea floor, such as a sunken ship or a mine, it is possible to detect the object by using SSS images. However, the SSS using a narrow beam is excellent in spatial resolution but uses high-frequency sound, so that sound does not propagate below the sea floor, and therefore information on a buried object below the sea bottom (hereinafter also referred to as a buried target). Can not get.

On the other hand, a sub-bottom profiler (SB
P (Sub-Bottom Profiler) uses a low frequency with good seabed permeability and is capable of imaging echoes from the stratum below the seabed. However, since a low frequency broad beam is used, the spatial resolution is inferior.
It is not possible to obtain high-definition video such as

When a small object buried in seabed mud or sand, that is, a buried target is to be searched and detected, SSS and S
A search method that combines the advantages of BP is needed. In other words, it is possible to use the same low frequency as SBP,
A sonar method that can provide high resolution equivalent to that of the above is required.

As such a sonar system, there is a synthetic aperture sonar (SAS). SAS is a system that simultaneously realizes low frequency and high resolution, and achieves high spatial resolution by operating like a SSS using a low frequency transducer, and obtains echoes of buried targets as well as exposure targets. be able to.

A method of searching for a buried target using such a SAS is proposed in, for example, Japanese Patent Application Laid-Open Nos. 10-153657 and 2000-249760. In these systems, both the exposure target and the buried target are detected by the SAS alone, and the two cannot be clearly distinguished. Therefore, the SAS and SSS are used in combination, and the images obtained by both are compared to determine the exposure on the seabed. It is characterized in that the target and the burial target are configured to be separated.

[0007]

As described above, SBP
In the sonar method using the SAS alone, which can use a low frequency equivalent to that of SSS and obtain a high resolution equivalent to SSS, echo can be obtained equally from both the exposure target and the buried target, and sufficient information to distinguish both can be obtained. Since it cannot be obtained, a sonar system using both SAS and SSS has been conventionally proposed. In such a sonar system, two sonar devices need to be deployed and operated at the same time.
There is a problem in that it is complicated and is extremely complicated in operation and maintenance.

(Object of the Invention) It is an object of the present invention to provide a buried object detecting method and a buried object detecting sonar capable of distinguishing an exposure target and a buried target by a single sonar method.

Another object of the present invention is to provide a buried object detection method and a buried object detection sonar which can reduce the size and weight of the apparatus and simplify the operation and maintenance as compared with the conventional system.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a plurality of transducers are multiplexed by dividing the transducer in the vertical direction. Or a buried target. In addition, the vertical azimuth of the echo is estimated by performing a threshold process on a difference between a lag time between received signals of a plurality of transducers and a lag time theoretically obtained.

The buried object detecting method according to the present invention is directed to a buried object detecting method for detecting an object on the bottom of the water using a plurality of transducers for vertically transmitting and receiving a sound wave in a lateral direction. Estimated azimuth of the echo is calculated based on the received signal of the transmitter, and the theoretical azimuth of the echo from the water bottom with respect to the range or the delay time of the echo is theoretically calculated from the baseline d between the transmitter and the receiver, the water bottom altitude h and the water bottom topographical information. Calculated as the azimuth, find the difference between the estimated azimuth and the theoretical azimuth, and whether the echo is from a buried object on the water floor or from an exposed object, depending on whether the absolute value of the difference exceeds a predetermined threshold. Is determined.

Further, in the above invention, the estimated azimuth is calculated after performing a synthetic aperture process on a received signal. Furthermore, as the information of the estimated azimuth and the theoretical azimuth, a lag time time series that is a difference between echo delay times between a plurality of transducers is used, and the lag time time series of the estimated azimuth is the plurality of lag times. It is characterized in that it is generated by cross-correlation processing on the received signal of the transducer.

[0013] The buried object detection sonar of the present invention is a buried object detection sonar for detecting an object at the bottom of the water using a plurality of transducers that are vertically divided and transmit and receive a sound wave in a lateral direction. A level processing unit for detecting an echo from an object on the bottom of the water from a signal received by the transmitter, an estimation direction unit for calculating the direction of the echo from the reception signals of the plurality of transducers, a baseline d between the transmitter and the receiver, h and underwater topographic information, a logical azimuth unit for calculating the theoretical azimuth of the echo from the water bottom with respect to the range or the delay time of the echo as the theoretical azimuth, and obtaining a difference between the estimated azimuth and the theoretical azimuth; A threshold processing unit that determines whether the detected echo is from a buried object or an exposed object on the water floor based on whether or not the absolute value of the detected echo exceeds a predetermined threshold. The features.

The apparatus further comprises a synthetic aperture processing section for performing synthetic aperture processing on the received signals of the plurality of transducers, respectively.
The level processing unit detects an echo based on an output from the synthetic aperture processing unit, and the estimation processing unit calculates the estimated orientation based on an output from the synthetic aperture processing unit. In addition, as the information of the estimated azimuth and the theoretical azimuth, a lag time time series that is a difference between echo delay times between a plurality of transducers is used, and the lag time time series of the estimated azimuth is the plurality of lag times. It is characterized in that it is generated by cross-correlation processing on the received signal of the transducer.

Further, the buried object detection system of the present invention is a buried object detection system for detecting the bottom of the water by using a plurality of transducers for transmitting and receiving sound waves in the vertical direction and transmitting and receiving sound waves in the lateral direction. Based on the water bottom topography and the water bottom altitude, logical time series information composed of logical azimuth information and distance information on the echo of the transmitted sound wave from the water bottom is calculated, and a plurality of times based on the echo of the transmitted sound wave from the water bottom are calculated. Detecting a water bottom object by a received signal from the transmitter / receiver, generating reception time-series information of the azimuth information and distance information of the echo by performing a cross-correlation process of the received signal, the logical time-series information and It is characterized in that it is determined whether the underwater object exists on the underwater surface or under the underwater surface by comparison with the reception time-series information.

More specifically, assuming a SAS that is operated in the same manner as a general SSS, an exposure target and a burial target (for example, 7 and 8 in FIG. 1) while irradiating sound obliquely from the seabed altitude h. Search for A transducer (for example, 2 in FIG. 1) mounted on a platform (for example, 1 in FIG. 1) towed underwater from a tugboat or the like has a vertical length (for example, 2 in FIG. 1).
d) and has a certain degree of vertical directivity.
Resolution in the range and azimuth directions is realized by synthetic aperture processing. In the echo level processing (for example, 3 in FIG. 1), a point at which the level exceeds a certain threshold is recorded as a target by processing similar to general SSS. Next, the receiving direction is individually processed by the transducer array separated into two in the vertical direction, and the estimated orientation is calculated (for example, 4 in FIG. 1). The azimuth estimation can be realized by cross-correlation processing of the received signals of the two systems.
On the other hand, since the theoretical echo direction in the range R can be calculated from the base line d between the transmitter and the receiver, the seafloor altitude h, and the like, this is calculated as the theoretical direction (for example, 5 in FIG. 1). The difference between the estimated azimuth of the received signal and the theoretical azimuth is obtained, and threshold processing is performed on the absolute value of the difference (for example, 6 in FIG. 1). If the absolute value of the difference is less than a certain threshold, it is determined as an exposure target, and if it is more than the threshold, it is determined as a burial target. A direction based on cross-correlation processing is used for azimuth estimation. This is to estimate the delay time of the signal received by the two receiving systems according to the azimuth. Received signal input (for example, 4 in FIG. 4)
11 and 412), a cross-correlation process between the two signals (for example, 413 in FIG. 4) is performed, and the peak value thereof is detected (for example, 42 in FIG. 3). Since the lag time at which the cross-correlation peak value appears corresponds to the amount of time delay between the two signals, the time series of the echo azimuth estimation amount can be obtained by continuously performing this processing in a time series. By calculating the theoretical azimuth in the form of a lag time between the received signals of the two transducers, the difference from the estimated azimuth can be easily determined.

(Operation) The estimated azimuth of the received signal is calculated by performing cross-correlation processing of the received signals of the two systems received by the two transmitters / receivers separated in the vertical direction. From the base line d between the transmitter and the receiver, the sea floor altitude h, etc., the theoretical azimuth of the range R or the delay time τ at which the echo arrives is calculated as the theoretical azimuth, and the estimated azimuth measured from the actual received signals of the two systems and Take the difference from the theoretical orientation,
Depending on whether the absolute value of the difference exceeds a predetermined threshold,
It is determined whether the detected target is a buried target or an exposure target.
As information of the estimated azimuth and the theoretical azimuth of the received signal, a lag time series which is a difference between lag times at the time of reception of the two transducers with respect to the detected target can be used. The difference information between the azimuth and the theoretical azimuth is detected as a deviation of each lag time time series.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for detecting a buried object and a sonar for detecting a buried object according to the present invention will be described in detail with reference to the drawings.

(Description of Configuration) FIG. 1 is a diagram showing a basic configuration of a method for detecting a buried object and a sonar for detecting a buried object according to the present embodiment. The buried object detection sonar is mounted on a platform 1 that is towed underwater by a tugboat or the like in a direction perpendicular to the plane of the figure, and transmits and receives echoes from the seabed while irradiating sound obliquely to the seabed. 2, a level processing unit 3 for detecting a target from the signal received by the transmitter / receiver 2, an estimation direction unit 4 for estimating the receiving direction of the echo,
A logical azimuth unit 5 for calculating logical information about the receiving direction of the echo, and a threshold processing unit 6 for determining whether the target exists on the sea floor or below the sea floor by using a threshold,
The target 7 to be exposed and the target 8 to be buried are searched for from the received signal received by the transducer 2. The details of each part are as follows.

The transducer 2 has an opening length of 2d in the vertical direction, and is divided into two arrays 11 and 12 having the same dimension in the vertical direction, and has a predetermined vertical directivity.

The level processing unit 3 determines a signal level using a threshold value for a signal obtained by adding two received signals from the arrays 11 and 12, and regards an echo signal exceeding the threshold value as an echo from a target. Has the function of detecting. The estimation direction unit 4 has a function of performing cross-correlation processing of two received signals and estimating time-series reception direction information from echoes detected from the received signals based on the result of the correlation processing.

The logical azimuth unit 5 includes a base line d between the transmitter and the receiver, which is a distance between the center positions of the two arrays 11 and 12 of the same size which constitute the transmitter and the receiver, and a distance from the transmitter and the receiver to the sea floor. Seafloor altitude h and seafloor topography (horizontal landform)
Based on this information, information on the reception direction of the echo for each delay time (or distance from the reflection position) of the echo from the seabed reflection position is calculated and held as time-series logical direction information.

The threshold processing unit 6 is configured to determine, with respect to the echo from the target detected by the level processing unit 3, the time-series reception direction information estimated by the estimation direction unit 4 and the time-series reception direction stored in the logical direction unit 5. Generate a difference with the information of the logical azimuth, compare the absolute value of the difference with a predetermined threshold, depending on whether or not exceeds the threshold, the target is under the seabed surface or on the seabed surface Determine if it exists.

Next, the principle of object (target) detection by the buried object detection method and the buried object detection sonar of the present invention will be described.

FIG. 2 is a diagram showing a method of determining an exposure target and a buried target on the seabed according to the present invention. The two transducers A and B are assumed to be arranged in a vertical direction with respect to each other. The base line length between the transducers, which is the distance between the centers, is d, the phase center point of the transmission of both transducers is P, and the seafloor height h (Horizontal sea floor).

As shown in FIG. 2A, when an echo at an angle θ with respect to the horizontal direction is received from a slant range R at an arbitrary position on the sea floor, the reception timing at each of the transducers A and B is It is proportional to the sound propagation distances OA and OB.

Accordingly, the difference between the reception timings of the two received signals (the delay time difference between the two received signals, hereinafter referred to as lag time) ΔT is expressed as follows.

ΔT = AB ′ / C ≒ d · sin θ / C (1) Here, an approximation of R >> d is used, and C is the underwater sound velocity. If there is no ray refraction in the direct path, Δ
T is expressed as follows using the distance R or the elapsed time τ from the reflection of the transmitted wave for the angle θ.

ΔT = (d / C) · h / R = (d / C) · h / (C · τ) (2) This is a case where an echo from the sea bottom is assumed.
It corresponds to time-series information of the reception direction of the echo from each sea bottom position, and can be logically calculated based on the base line length d between the transmitter and the receiver, the sea bottom altitude h, and the sea bottom topography (horizontal sea bottom, etc.). This is delay time information (hereinafter referred to as theoretical lag time time series).

By the way, when the echoes from the sea bottom are received by the transducers A and B and the cross-correlation of both received signals is calculated, a correlation peak is obtained near the point represented by the equation (2). That is, when there is an exposure target at an arbitrary O point on the sea floor as shown in FIG. 2A, the actual received signal also has a lag time (hereinafter, referred to as a reception lag time time series) close to the equation (2). Will be.

FIG. 2 (b) shows an echo received from a target Oo 'buried on the seabed at a specific elapsed time τo after an acoustic wave is transmitted and an echo received from the seabed Oo at the same elapsed time τo. It is a figure showing a relation. Here, assuming that the sound velocity at the sea bottom is Cs, the sound ray is refracted at the sea bottom as shown in FIG.

Since the reception timings of both echoes are simultaneous, the following relational expression is obtained.

Ro / C = Rs / Cs + Ro ′ / C (3) Accordingly, sin θo ′ is sin θo ′ = h / Ro ′ = h / (Ro−α · Rs), α = C / Cs (4) From this relationship, the lag time ΔTo ′ when receiving the echo from the buried target Oo ′ is expressed as follows.

ΔTo ′ = (d / C) · h / (Ro−α · Rs) (5) On the other hand, the lag time ΔTo when receiving an echo from the sea floor Oo is given by the following equation (2). It is represented as

ΔTo = (d / C) · h / Ro (6) As can be seen from a comparison between the equations (5) and (6), the lag time when the echo from the buried target is received is Lag time from the calculated lag time assuming echoes from the sea floor.

According to the present invention, the detected target is compared with the reception lag time series and the logical lag time series to detect and judge the presence or absence (degree) of a lag time shift, so that the target can be detected on the sea floor. Judge whether it is a burial target below or an exposure target above the sea floor.

That is, as a result of performing the level threshold processing in the level processing unit 3 of the buried object detection sonar shown in FIG. 1, a target is detected on the sonar image, and the threshold processing unit 6 applies a lag time threshold to the target. By performing the processing, it is determined whether the target is an exposure target or a burial target.

FIGS. 3 and 4 are diagrams showing a more detailed configuration of the signal processing unit in the buried object detection sonar of the present embodiment.

As shown in FIG. 3, at the subsequent stage of each of the arrays 11 and 12, a transmission / reception switching device 1 for switching between transmission and reception is provided.
3 and 14 are respectively disposed, and the transmission / reception switching devices 13 and 14 are provided.
As a transmission system for outputting a transmission signal, the transmission system comprises a waveform generation unit 21 for generating a transmission signal, and a power amplifier 22 for amplifying the transmission signal.
3 and 14 to the arrays 11 and 12 simultaneously.

The transmission signal (signal waveform) is LFM (Linear Frequency Modulation) modulated so that the frequency of the transmission signal changes linearly in order to improve range resolution by performing range compression in reception processing. ) Is used.

In the receiving system, the processing system is separated for each array.
Preamplifiers 15 and 16 with gain adjustment function,
Synthetic aperture processing units 31 and 32 that perform range compression and azimuth direction directivity synthesis generate two upper and lower narrow beam reception signals. In other words, by the synthetic aperture processing,
Improves range and azimuth resolution.

The second stage of the synthetic aperture processing units 31 and 32 is a system for performing a level threshold processing for echo (level threshold processing system) and a system for performing a lag time difference threshold processing between reception lag times of the respective transducers (lag). (Time difference threshold processing system).

The level threshold processing system includes an adder 33 for adding two received signals, and a level threshold processor 34 for comparing the added received signal with a preset level threshold Th1.
It is composed of

The lag time difference threshold processing system includes a cross-correlation processing unit 41 for obtaining a cross-correlation between two received signals, and a peak detection unit 4 for detecting peaks of the correlation processing results and arranging them in a time series.
2, a reference generation unit 43 for generating a theoretical lag time series corresponding to the operation of the waveform generation unit 21, and a lag time threshold Th2 preset for the lag time difference.
And a level threshold processing unit 34 that performs threshold processing using the.

The reference generation unit 43 has a gyro 45 for measuring an angle in order to detect and correct the inclination of the transducer, and the reference generation unit 43 and the gyro 4
5 constitute the logical orientation unit 5 shown in FIG.

(Explanation of Operation) Next, the processing operation from transmission to reception in the buried object detection sonar of this embodiment will be described in detail with reference to FIGS.

The waveform generator 21 generates a transmission signal (transmission waveform), amplifies the transmission signal to a predetermined transmission level by the power amplifier 22, and transmits / receives the signals to the transmitter / receivers 11 and 12 via the transmission / reception switching circuits 13 and 14. Send to The transducers 11, 12 are:
The transmission signal is subjected to electric / acoustic conversion and transmitted as underwater sound waves. The transmitted sound wave is reflected at the sea floor or at the target, and returns to the transducers 11 and 12 as echo signals over time from the reflected wave at the nearest point to the reflected wave at a distance in order.

The transducers 11 and 12 receive the returned echo signal, perform acoustic / electrical conversion, and output the signals as independent time-series received signals, and transmit / receive switching circuits 13 and 14.
Are supplied to the preamplifiers 15 and 16 via the. The preamplifiers 13 and 14 perform dynamic gain adjustment by controlling AGC (Auto-Gain Control) or TVG (Time Varying Gain), and amplify and adjust so that the signal level of a time-series received signal becomes constant. , Synthetic aperture processing units 31, 3
Output to 2.

The synthetic aperture processing sections 31 and 32 receive the amplified reception signals, perform range compression and azimuth compression processing, and generate a synthetic aperture processing signal that becomes a high-resolution sonar image by using a level threshold processing system and a lag in a subsequent stage. It is sent to the time difference threshold processing system (s1, s2).

In the level threshold processing system, the adder 33 adds the two synthetic aperture processing signals (s3), and performs vertical directivity synthesis to further improve the SR ratio.
The level threshold processing unit 34 compares the signal level with a preset threshold Th1, and records a signal in which the synthetic aperture processing signal exceeds the threshold as a target (echo from the target) (s4, s5).

In the lag time difference threshold value processing system, the cross-correlation processing section 41 calculates the cross-correlation between the two synthetic aperture processing signals 1 and 2 shown in FIG. 4 (s6), and outputs the correlation processing result to the peak detection section 42. Output. The peak detector 42 records the time-series change of the peak value of the correlation processing result (s7). At the same time, the reference generation unit 43 calculates the theoretical lag time series represented by the formula (2) (s8), generates a difference from the reception lag time series, and outputs the difference to the lag time threshold processing unit 44. The lag time threshold processing unit 44 presets a predetermined threshold (lag time threshold) Th2 for the lag time difference, and sets the exposure target and the lag time threshold Th2 when the lag time difference does not exceed the lag time threshold Th2. If it exceeds, it is determined that it is a burial target (s9, s10).

That is, the lag time difference takes a value close to 0 for the echo from the sea floor, ie, the echo of the exposure target, but largely deviates from 0 for the echo of the buried target. Therefore, if the lag time difference at the target position previously recorded by the level threshold processing is close to 0, the exposure target, 0
If it is significantly different from the target, it can be determined that the target is buried. Therefore, by performing the determination process as a threshold process based on a preset lag time threshold, it is possible to determine and output whether the detected target is an exposure target or a buried target.

The theoretical lag time of equation (2) in the above description of the operation is based on the premise that the transducers 11 and 12 are arranged in a vertical direction. This condition is not always satisfied. Therefore, in the present embodiment, a gyro capable of detecting the tilt angle with high accuracy is mounted, and the roll angle of the platform (ie, the transducer) is constantly measured to perform the angle correction processing. This correction process can be configured to be performed in the reference generation unit 43.

(Other Embodiments) In the above-described embodiment, an example has been described in which the spatial resolution is improved by the synthetic aperture processing, but this configuration is replaced by directivity synthesis using a normal line array. It may be configured as follows.
In this case, since it is necessary to generate a low-frequency narrow beam, only the array portion is enlarged.

Further, a configuration can be adopted in which a low-frequency narrow beam is realized by a parametric array instead of the synthetic aperture system. In this case, the configuration is such that the transmission power is increased from the relation of electric / sound conversion efficiency.

In the above embodiment, the example in which the transducer is divided into two in the vertical direction has been described. However, the transducer can be divided into three or more in the vertical direction. In this case, by increasing the baseline length, the angular resolution (lag time estimation accuracy) in the vertical direction of the array is increased, so that an improvement in performance can be expected.

In the above embodiment, the operation of the level threshold processing system and the operation of the lag time difference threshold processing system are performed only when a target (object) is detected as a result of the operation and display of the level threshold processing system. The configuration may be such that the operation for determining whether the target is an exposure target or a buried target is performed by the time difference threshold processing system, or the processing operations of both processing systems may be performed in parallel. In addition, although the seabed topography is shown as a horizontal plane for the sake of explanation, the above-mentioned logical lag time series is used for arbitrary terrain based on known terrain such as sloped terrain or terrain information obtained from the level threshold processing system. Can be calculated.

[0058]

According to the present invention, by extracting the difference between the theoretical echo azimuth and the actual echo azimuth, it is possible to estimate whether the target is on or below the sea floor. With such a configuration, it is possible to automatically determine whether the detection target is an exposure target or a buried target using a single sonar method.

In order to determine the exposure target and the burial target,
In the conventional method, it is necessary to simultaneously operate two types of sonar methods using low-frequency and high-frequency sound waves, which cannot avoid an increase in the number of transducers and transmitting / receiving devices. Since it is not necessary to use the sonar method together, it is possible to reduce the size, simplification and weight of the device,
It is possible to reduce the complexity of operation, operation, and maintenance.

[0060]

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a method for detecting a buried object and a sonar for detecting a buried object according to the present embodiment.

FIG. 2 is a diagram illustrating a state of sound wave propagation by an exposure target and a buried target, and a method of determining an exposure target and a buried target on the seabed according to the present invention.

FIG. 3 is a diagram showing a more detailed configuration of a signal processing unit in a buried object detection sonar according to the present embodiment.

FIG. 4 is a block diagram showing a method for acquiring a lag time series.

FIG. 5 is a diagram showing an operation flow of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Buried object detection sonar 2 Transceiver 3 Level processing part 4 Estimated azimuth part 5 Logical azimuth part 6 Threshold processing part 7 Exposed object on the seabed 8 Buried object on the seabed 11, 12 Divided transducer array 15, 16, 22 Power amplifier 21 Waveform generation unit 31, 32 Synthetic aperture processing unit 33 Addition unit 34 Level threshold processing unit 41 Cross-correlation processing unit 42 Peak detection unit 43 Reference processing unit 44 Lag time threshold processing unit 45 Gyro

Claims (8)

[Claims] 1. A buried object detection method for detecting an object on the bottom of a water using a plurality of transducers for transmitting and receiving sound waves in a vertical direction and transmitting and receiving a sound wave in a lateral direction, wherein an echo based on reception signals of the plurality of transducers is provided. From the baseline d between the transmitter and the receiver, the water bottom altitude h, and the water bottom topography information, the theoretical direction of the echo from the water bottom with respect to the range or the delay time of the echo is calculated as the theoretical direction, and the estimation is performed. Finding the difference between the azimuth and the theoretical azimuth, and determining whether the echo is from a buried object or an exposed object on the water floor by determining whether the absolute value of the difference exceeds a predetermined threshold. Buried object detection method. 2. The estimated azimuth is calculated after performing a synthetic aperture process on a received signal.
The method for detecting a buried object according to the description. 3. The lag time series, which is a difference between delay times of echoes between a plurality of transducers, is used as the information of the estimated azimuth and the theoretical azimuth. Buried object detection method. 4. The buried object detecting method according to claim 3, wherein the lag time series as the information of the estimated azimuth is generated by performing a cross-correlation process on the reception signals of the plurality of transducers. 5. A buried object detection sonar for detecting an object at the bottom of the water using a plurality of transducers for transmitting and receiving sound waves in the vertical direction and transmitting and receiving sound waves in the lateral direction, wherein: A level processing unit that detects an echo from an object, an estimated azimuth unit that calculates the azimuth of the echo from the reception signals of the plurality of transducers, and a baseline d between the transducers, a water bottom altitude h and water bottom topography information, A logical azimuth unit for calculating the theoretical azimuth of the echo from the water bottom with respect to the range or the delay time of the echo as a theoretical azimuth, and calculating a difference between the estimated azimuth and the theoretical azimuth, and an absolute value of the difference being a predetermined threshold A threshold processing unit for determining whether the detected echo is from a buried object or an exposed object on the water floor depending on whether the detected echo exceeds the threshold value or not. Over. 6. A synthetic aperture processing section for performing synthetic aperture processing on received signals of the plurality of transducers, wherein the level processing section detects an echo based on an output of the synthetic aperture processing section, and the estimation processing section 6. The buried object detection sonar according to claim 5, wherein the estimated azimuth is calculated by an output of a synthetic aperture processing unit. 7. A lag time series, which is a difference between echo delay times between a plurality of transducers, as the information on the estimated orientation and the theoretical orientation. Buried object detection sonar. 8. The buried object detection sonar according to claim 7, wherein the lag time series as the information of the estimated azimuth is generated by a cross-correlation process on the reception signals of the plurality of transducers.